This invention relates generally to the synthesis of carbon, particularly in an activated form, from sludge and, in particular, from waste sludge such as composed of biosolids and the like. One particular aspect of the invention relates generally to the synthesis of carbon-based catalysts, from a sludge material such as produced in paper mill processing and which catalysts may be useful or effective for removal of gaseous pollutants such as NOx, SO2, H2S and various organic vapors, for example, from process streams brought into contact therewith.
In view of factors such as increased relative quantities of sludge materials such as produced or formed at wastewater treatment, paper mill processing and the like facilities and limited disposal areas for such sludge materials, there is an increasing need and demand for processing techniques whereby such sludge materials can be transformed or converted into other, possibly more desirable and useful, materials.
Biosolids is the waste sludge such as produced at wastewater treatment facilities and as may result from various bioreactions. Biosolids, also sometimes called or referred to as the sludge or residue of sewage treatment processes, are typically nutrient-rich by-products of specially treated or stabilized wastewaters originating from municipalities, industries or storm water runoff, for example, and typically produced in relatively high mass rates.
Activated carbon is a frequently used adsorbent material and has virtually displaced many other materials in use as adsorbents in various solvent recovery systems. Activated carbon is a generally superior adsorbent at least in part because of desirable surface properties. The unique adsorption capability of activated carbons is generally related to such carbon materials having a high adsorption capacity and a high degree of surface porosity and such as may relate to carbon materials desirably having relatively high surface areas and significant microporous structure. In general, pores are classified by size in one of three categories or classes: micropores (pores having a width less than 2 nm), mesopores (pores having a width of 2 nm and 50 nm), and macropores (pores having a width in excess of 50 nm).
Activated carbons are used extensively for or in various industrial applications including: solvent recovery, gas refining, air purification, exhaust desulfurization, deodorization and gas separation and recovery, for example. The application of activated carbons in water treatment includes: removal of color, odor, taste or other undesirable impurities from water; treatment of domestic and industrial wastewaters; and collection and recovery of solutes such as gold and silver, for example. In addition, activated carbons have found application as catalysts in various chemical processes.
In practice, the activity as well as possibly the effectiveness of such carbon material in particular adsorbent or catalyst applications may be limited by either or both the surface area and porosity of the activated carbon material. The production or formation of such activated carbon material from selected chemical processing waste streams has been generally limited or restricted due to limitations in either or both the surface area and porosity of the resulting activated carbon material.
Thus, there is a need and a demand for economical and environmentally sound solutions to biosolids management and reuse at treatment facilities at various locations in the world. In particular, there is a need and a demand for techniques whereby such raw material or wastewater streams can be processed or otherwise treated such as to produce or form activated carbon of either or both increased surface area and increased microporosity. Further, there is a need and a demand for activated carbon having either or both increased surface area and increased microporosity and such as formed from such process streams.
Further, the possible or potential uses of waste sludges such as produced by or resulting from the paper mill industry have, in practice, been relatively limited. As a result, such sludges may create or result in significant disposal problems and concerns as, for example, the associated expenses can be significant. In view of the above, there is a need and a demand for an economical and efficient approach for the recycling or use of waste sludges such as produced by the paper mill industry, for example.
A general object of the invention is to provide an improved method for producing activated carbon.
Another general object of the invention is to provide an activated carbon of high surface area and microporosity such as formed from a carbon-containing sludge raw material.
Yet another general object of another aspect of the invention is to provide an improved method for producing carbon-based catalysts and, in particular, an improved synthesis of carbon-based catalysts from sludge material.
A more specific objective of the invention is to overcome one or more of the problems described above.
A general object of the invention can be attained, at least in part, and the invention encompasses in accordance with one embodiment a specified method for producing activated carbon from a carbon-containing sludge raw material. Such method includes a pretreatment step of drying a carbon-containing sludge followed by crushing and sieving to form a dried sludge material. The dried sludge material is chemically activated to form a chemically-activated sludge material which is crushed and dried to form a dry crushed chemically-activated material. The dry crushed chemically-activated material is subjected to high energy light activation in an environment having a relative humidity of at least 50 percent to form an energy-treated chemically-activated sludge material. The energy-treated chemically-activated sludge material is pyrolyzed at an elevated temperature effective to form a pyrolyzed sludge material of increased microporosity which is cooled, crushed, rinsed, dried and then physically activated forming the activated carbon.
The prior art fails to provide as simple, economical and environmentally sound solution as desired to the management and reuse of sludge materials such as biosolids at treatment facilities at various locations in the world. More particularly, the prior art fails to provide for the synthesis of activated carbon of either or both increased surface area and increased microporosity from sludge materials such as composed of biosolids and the like.
The invention further comprehends a method for producing activated carbon from a carbon-containing biosolids sludge raw material. In accordance with one such method, a carbon-containing biosolids sludge is dried, crushed and sieved to form a dried sludge material. An aqueous solution of a metal-based chemical activation agent is added to the dried sludge material to form a chemically-activated sludge material containing at least a portion of the metal of the chemical activation agent. The chemically-activated sludge material is crushed and dried to form a dry crushed chemically-activated material. The dry crushed chemically-activated material is exposed to light having an average intensity of 50 microwatts and in an environment having a relative humidity of about 60 percent to about 70 percent to promote oxidation of metal contained within the dry crushed chemically-activated material forming a light and humidity treated activated sludge material. The light and humidity treated chemically-activated sludge material is pyrolyzed at a temperature in the range of about 775xc2x0 C. and about 825xc2x0 C. to form a pyrolyzed sludge material of increased microporosity. The pyrolyzed sludge material is subsequently cooled, crushed, rinsed and dried. The so processed sludge material is then treated with an activating gas to remove residual gases, followed by heating the treated pyrolyzed sludge material in the presence of the activating gas to at least partially oxidize the surface and expand the pores of the treated pyrolyzed sludge material forming activated carbon.
The invention still further comprehends activated carbon of high surface area and microporosity formed from such carbon-containing sludge raw materials using such a process.
As used herein, references to a sludge material as having a xe2x80x9chigh organic contentxe2x80x9d are to be understood to sludge materials which are composed of at least about one-third organic materials and, preferably sludge materials having an organic content in the range of about 35 to about 75 weight percent.
A general object of at least certain aspects of the invention can be attained, at least in part, through a specified method for synthesizing a carbon-based catalyst from a carbon-containing sludge raw material. Such method, in accordance with one specific embodiment of the invention, includes the steps of:
drying, crushing and sieving a carbon-containing sludge to form a dried sludge material;
chemically activating the dried sludge material with at least one metal-based activating agent to form a chemically-activated sludge material;
drying and crushing the chemically-activated sludge material to form a dry crushed chemically-activated material;
exposing the dry crushed chemically-activated material to light in an environment having a relative humidity of at least 50 percent to form a light-treated chemically-activated material;
pyrolyzing the light-treated chemically-activated material at an elevated temperature effective to form a pyrolyzed material of increased microporosity, as compared to the light-treated chemically-activated material prior to pyrolysis; and
cooling, crushing, rinsing and drying the pyrolyzed material to form the carbon-based catalyst.
The prior art generally fails to provide an approach for the recycling or use of waste sludges and such as results, produces or supplies carbon-based catalysts in a manner as economical and efficient as may be desired. In particular, the prior art generally fails to provide a method for synthesizing a carbon-based catalyst from a carbon-containing sludge raw material, such as produced by the paper mill industry, for example, and which catalyst may be effective in the reduction or removal of one or more gaseous pollutants such as NOx, for example, from a process stream appropriately brought into contact therewith.
The invention also comprehends a method for synthesizing a carbon-based NOx reduction catalyst from a carbon-containing sludge raw material. In accordance with one specific embodiment of the invention, such a method includes the steps of:
drying, crushing and sieving a carbon-containing sludge to form a dried sludge material;
chemically activating the dried sludge material with a NOx reduction chemical activating agent which includes a first metal-based activating agent which includes zinc and a second metal-based activating agent which includes iron to form a chemically-activated sludge material;
drying and crushing the chemically-activated sludge material to form a dry crushed chemically-activated material;
exposing the dry crushed chemically-activated material to light in an environment having a relative humidity of at least 50 percent to form a light-treated chemically-activated material;
pyrolyzing the light-treated chemically-activated material at an elevated temperature effective to form a pyrolyzed material of increased microporosity, as compared to the light-treated chemically-activated material prior to pyrolysis; and
cooling, crushing, rinsing and drying the pyrolyzed material to form the carbon-based NOx reduction catalyst.
Other objects and advantages will be apparent to those skilled in the art from the following detailed description taken in conjunction with the appended claims and drawings.